DL-Art-School/codes/trainer/lr_scheduler.py

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import math
from collections import Counter
from collections import defaultdict
import torch
from torch.optim.lr_scheduler import _LRScheduler
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def get_scheduler_for_name(name, optimizers, scheduler_opt):
schedulers = []
for o in optimizers:
# Hack to support LARC, which wraps an underlying optimizer.
if hasattr(o, 'optim'):
o = o.optim
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if name == 'MultiStepLR':
sched = MultiStepLR_Restart(o, scheduler_opt['gen_lr_steps'],
restarts=scheduler_opt['restarts'],
weights=scheduler_opt['restart_weights'],
gamma=scheduler_opt['lr_gamma'],
clear_state=scheduler_opt['clear_state'],
force_lr=scheduler_opt['force_lr'])
elif name == 'ProgressiveMultiStepLR':
sched = ProgressiveMultiStepLR(o, scheduler_opt['gen_lr_steps'],
scheduler_opt['progressive_starts'],
scheduler_opt['lr_gamma'])
elif name == 'CosineAnnealingLR_Restart':
sched = CosineAnnealingLR_Restart(
o, scheduler_opt['T_period'], scheduler_opt['warmup'], eta_min=scheduler_opt['eta_min'],
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restarts=scheduler_opt['restarts'], weights=scheduler_opt['restart_weights'])
else:
raise NotImplementedError('Scheduler not available')
schedulers.append(sched)
return schedulers
# This scheduler is specifically designed to modulate the learning rate of several different param groups configured
# by a generator or discriminator that slowly adds new stages one at a time, e.g. like progressive growing of GANs.
class ProgressiveMultiStepLR(_LRScheduler):
def __init__(self, optimizer, milestones, group_starts, gamma=0.1):
self.milestones = Counter(milestones)
self.gamma = gamma
self.group_starts = group_starts
super(ProgressiveMultiStepLR, self).__init__(optimizer)
def get_lr(self):
group_lrs = []
assert len(self.optimizer.param_groups) == len(self.group_starts)
for group, group_start in zip(self.optimizer.param_groups, self.group_starts):
if self.last_epoch - group_start not in self.milestones:
group_lrs.append(group['lr'])
else:
group_lrs.append(group['lr'] * self.gamma)
return group_lrs
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class MultiStepLR_Restart(_LRScheduler):
def __init__(self, optimizer, milestones, restarts=None, weights=None, gamma=0.1,
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clear_state=False, force_lr=False, last_epoch=-1):
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self.milestones = Counter(milestones)
self.gamma = gamma
self.clear_state = clear_state
self.restarts = restarts if restarts else [0]
self.restarts = [v + 1 for v in self.restarts]
self.restart_weights = weights if weights else [1]
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self.force_lr = force_lr
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assert len(self.restarts) == len(
self.restart_weights), 'restarts and their weights do not match.'
super(MultiStepLR_Restart, self).__init__(optimizer, last_epoch)
def get_lr(self):
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if self.force_lr:
return [group['initial_lr'] for group in self.optimizer.param_groups]
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if self.last_epoch in self.restarts:
if self.clear_state:
self.optimizer.state = defaultdict(dict)
weight = self.restart_weights[self.restarts.index(self.last_epoch)]
return [group['initial_lr'] * weight for group in self.optimizer.param_groups]
if self.last_epoch not in self.milestones:
return [group['lr'] for group in self.optimizer.param_groups]
return [
group['lr'] * self.gamma**self.milestones[self.last_epoch]
for group in self.optimizer.param_groups
]
# Allow this scheduler to use newly appointed milestones partially through a training run..
def load_state_dict(self, s):
milestones_cache = self.milestones
super(MultiStepLR_Restart, self).load_state_dict(s)
self.milestones = milestones_cache
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class CosineAnnealingLR_Restart(_LRScheduler):
def __init__(self, optimizer, T_period, warmup=0, restarts=None, weights=None, eta_min=0, last_epoch=-1):
self.warmup = warmup
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self.T_period = T_period
self.T_max = self.T_period[0] # current T period
self.eta_min = eta_min
self.restarts = restarts if restarts else [0]
self.restarts = [v + 1 for v in self.restarts]
self.restart_weights = weights if weights else [1]
self.last_restart = 0
assert len(self.restarts) == len(
self.restart_weights), 'restarts and their weights do not match.'
super(CosineAnnealingLR_Restart, self).__init__(optimizer, last_epoch)
def get_lr(self):
step = self.last_epoch - self.warmup
if step <= 0:
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return self.base_lrs
elif step in self.restarts:
self.last_restart = step
self.T_max = self.T_period[self.restarts.index(step) + 1]
weight = self.restart_weights[self.restarts.index(step)]
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return [group['initial_lr'] * weight for group in self.optimizer.param_groups]
elif (step - self.last_restart - 1 - self.T_max) % (2 * self.T_max) == 0:
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return [
group['lr'] + (base_lr - self.eta_min) * (1 - math.cos(math.pi / self.T_max)) / 2
for base_lr, group in zip(self.base_lrs, self.optimizer.param_groups)
]
return [(1 + math.cos(math.pi * (step - self.last_restart) / self.T_max)) /
(1 + math.cos(math.pi * ((step - self.last_restart) - 1) / self.T_max)) *
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(group['lr'] - self.eta_min) + self.eta_min
for group in self.optimizer.param_groups]
if __name__ == "__main__":
optimizer = torch.optim.Adam([torch.zeros(3, 64, 3, 3)], lr=1e-4, weight_decay=0,
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betas=(0.9, 0.99))
##############################
# MultiStepLR_Restart
##############################
## Original
lr_steps = [200000, 400000, 600000, 800000]
restarts = None
restart_weights = None
## two
lr_steps = [100000, 200000, 300000, 400000, 490000, 600000, 700000, 800000, 900000, 990000]
restarts = [500000]
restart_weights = [1]
## four
lr_steps = [
50000, 100000, 150000, 200000, 240000, 300000, 350000, 400000, 450000, 490000, 550000,
600000, 650000, 700000, 740000, 800000, 850000, 900000, 950000, 990000
]
restarts = [250000, 500000, 750000]
restart_weights = [1, 1, 1]
scheduler = MultiStepLR_Restart(optimizer, lr_steps, restarts, restart_weights, gamma=0.5,
clear_state=False)
##############################
# Cosine Annealing Restart
##############################
## two
T_period = [500000, 500000]
restarts = [500000]
restart_weights = [1]
## four
T_period = [200000, 100000, 200000]
restarts = [200000, 300000]
restart_weights = [.5, .25]
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scheduler = CosineAnnealingLR_Restart(optimizer, T_period, warmup=10000, eta_min=1e-8, restarts=restarts,
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weights=restart_weights)
##############################
# Draw figure
##############################
N_iter = 500000
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lr_l = list(range(N_iter))
for i in range(N_iter):
scheduler.step()
current_lr = optimizer.param_groups[0]['lr']
lr_l[i] = current_lr
import matplotlib as mpl
from matplotlib import pyplot as plt
import matplotlib.ticker as mtick
mpl.style.use('default')
import seaborn
seaborn.set(style='whitegrid')
seaborn.set_context('paper')
plt.figure(1)
plt.subplot(111)
plt.ticklabel_format(style='sci', axis='x', scilimits=(0, 0))
plt.title('Title', fontsize=16, color='k')
plt.plot(list(range(N_iter)), lr_l, linewidth=1.5, label='learning rate scheme')
legend = plt.legend(loc='upper right', shadow=False)
ax = plt.gca()
labels = ax.get_xticks().tolist()
for k, v in enumerate(labels):
labels[k] = str(int(v / 1000)) + 'K'
ax.set_xticklabels(labels)
ax.yaxis.set_major_formatter(mtick.FormatStrFormatter('%.1e'))
ax.set_ylabel('Learning rate')
ax.set_xlabel('Iteration')
fig = plt.gcf()
plt.show()